Magnetic pickup construction for electrical musical instruments



March 2 5, 1941.

MAGNETIC PICKUP CONSTRUCTION FOR ELECTRICAL MUSICAL INSTRUMENTS FiledSept. 30, 1938 v z 1 [Llli/[IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII/IIII1M Zhwentor G. w.DEMUTH 2,235,983

Patented Mans, 1941 PATENT "OFFICE MAGNETIC PICKUP CONSTRUCTION FOREnscrnrcsr. MUSICAL msraumnn'rs Galan W. Demuth, Westviiie, N. 1.,assignor to Radio Corporation of America, a corporation Delaware 1Application September 30, 1938, Serial No. 232,526

6 Claims.

This invention relates to magnetic'pickup construction for use inelectric musical instruments and more particularly adapted for use inelectric pianos and other types of stringed musical in- D strumentshaving a plurality of magnetic strings.

Pianos and analogous instruments are'provided with a series of stringshaving diameters depending on the notes of the scale to be produced andthese strings particularly in pianos vary not only 10 in size but innumbers according to the notes. It

has heretofore been customary to make special pickups for each note ofthe scale of appropriate dimensions to most effectively pick up eachnote. Such an arrangement, however, is extremely unis satisfactorycommercially since the pickups are made to predetermined size and shapeand if they do not happen to be exactly suited to the particular notewhich is to be reproduced it is necessary to make a new pickup toaccommodate that par- 20 ticular note. Such an arrangement is extremelyunsatisfactory in the commercial production of electric musicalinstruments since it leaves a large portion of the pickups to behand-fitted and ad- Justed in each instrument. In pickups made ac- 25cording to my invention all the pickups may be made alike and may bereadily adjusted according to which note they are intended toaccommodate. I accomplish this result by making the pickups in the formof flat coils wound on a list 30 sott core and by similarly making theexciting magnets in the form of flat bars. Both the magnets and the softcore have a thickness commensurate with the width of'a single string andhave a breadth corresponding with the outside 35 dimension of thebroadest group of strings for a single note in the type of instrumentfor which the pickup is to be used.

One object of the invention is to provide an improved pickup having ahigh electric efficiency. 40 Another object of the invention is toprovide an improved type of pickup adapted to single strings or togroups of strings.

Another object of the invention is to provide an improved type vofpickup which may be readily manufactured in considerable quantities.

Another object of my invention is to provide a pick-up which is adaptedto efficiently pickup impulses from strings which are crowded closetogether.

50 Another object of my invention is to provide a pickup which is ofsuillcient size to be adapted to uniformly pick up the impulses fromlarge groups of strings.

Other and incidental objects of the invention 55 will be apparent tothose skilled in the art from a reading of the following specificationand an inspection of the accompanying drawing, in which- Fgure 1 is aside view of my improved pickup in proper relation to a string; 5

Figure 2 is a view from the bottom of Figure 1 showin the relation of asingle bass string to the pickup and the magnet;

Figure 3 is a view corresponding to Figure 2 by showing the relation ofthe pickup coil and magnet to a group of treble strings arranged as atriple unison; and

Figure 4 is a view corresponding to Figures 2 and 3 showing a pickupcoil and magnet as arranged in relation to a group of two strings in adouble unison as occurring in the middle range of the piano.

Referring first to Figure 1, a bass piano string is indicated at I, 2, Ibeing the-core and I being the winding thereon. A permanent magnet prefgerably of the material known as nlpermag for producing the necessarymagnetic field is shown at I, which is attached to a soft metal plate Iby means'of solder is indicated at I. A soft metal core I is likewiseattached to the plate 8 by means of a threaded extension II and the nutII. The plate 8' and core I are preferably made of cold rolled steel orsoft iron. Over this soft metal core there is provided a winding thaving the leads I. The magnet l and the core I are made inapproximately the shape shown and of a thickness as shown in Figure 2 ofthe same order as 'the width of one of the bass strings of the piano.The magnet is not necessarily, but is preferably flat, as shown, but itmay be of any other convenient shape. It is impractical to fasten themagnet 3 to the plate 8 in the same manner as the core I is fastened,due to the extreme hardness of the permanent. magnets used.

It will be apparent that in this arrangement 40 the largest possiblearea of the faces of the magnet I and of the core 5 are presented to thepiano string i, 2.

When it is desired to use the magnetic pickup for a triple unison in thehigher notes of the piano, the arrangement in Figure 3 is used where themagnet 3 and the core 5 are turned so as to be transverse of thestrings. In this case, due to the width of their faces the magnetequally affects all three strings while the pickup is equally affectedby all three strings.

In the application of the invention shown in Fig. 4, the pickup isapplied to a double unison in the middle range of the piano. In thiscase, both the magnet 3 and the soft core 5 with the pickup coil 6 areturned at such an angle as to adequately cover the two strings B3. Themembers 3 and 5 could, of course, be turned directly across the stringsl3, as shown in Fig. 3, but this would require more space and would notpermit the pickups to be placed as closely together as the pairs ofstrings for the several notes are usually placed, while the turning ofthe members 3 and 5 at an angle as shown, leaving them project only farenough beyond the strings to provide sufllcient pickup, minimizes thespace required without any decrease in efilciency.

The soft metal plates 8 of the pickups corresponding to the severalnotes of an instrument are, of course, mounted on an appropriate supportsuch, for example, as a long supporting strip which may reach completelyacross an entire group of strings.

It is apparent from the foregoing description that my improved pickupcan be applied to single strings or groups of strings and that the onlymodification necessary is the turning of the soft core and of thepolarizing magnet to the proper angle to the axis of the string orstring assembly.

Having now described my invention, I claim:

1. In a magnetic pickup for cooperation with one or more strings, thecombination of a magnetizable plate of soft material, a pair of polepieces secured endwise thereto, said pole pieces including a permanentmagnet thin in relation to its width and a second pole piece ofmagnetizable material also thin in relation to its width, a pickup coilsurrounding at least one of said pole pieces, both of said pole piecesbeing adapted to be placed at various angles to the axis of said plateaccording to the number of the vibrating elements they are intended tocooperate with.

2. In a magnetic pickup for cooperation with one or more strings, thecombination of a magnetizable plate of soft material, a pair of polepieces secured endwise thereto, one of said pole pieces being apermanent magnet thin in relation to its width, the other pole piecebeing of magnetizable material and thin in relation to its width, apickup coil surrounding at least one of said pole pieces, both of saidpole pieces being in parallel planes at'such angles to the axis of saidstrings as to most efiectively cooperate with either a single string ora group of strings, according to which the pickup is intended tocooperate with.

3. A magnetic pickup of the type described including a magnetizableplate of soft material, a

permanent magnet thin in relation to its width secured perpendicularlythereto. a core of soft magnetizable material thin in relation to itswidth and likewise secured perpendicularly to said plate, and a pickupcoil surrounding said soft core, both said magnet and said core beingadapted to be placed at various angles to the axis of said plateaccording to the member of the vibrating elements they are intended tocooperate with.

4. a magnetic pickup of the type adapted to cooperate with one or morestrings including a magnetizable plate of soft material, a permanentmagnet thin in relation to its width secured perpendicularly thereto, acore of soft magnetizable material thin in relation to its width andlikewise secured perpendicularly to said plate, and a pickup coilsurrounding said soft core, both said magnet and said core being inparallel planes at such angles to the axis of said strings as to mosteflectively cooperate with either a single string or a group of strings,according to which the pickup'is intended to cooperate with.

5. In combination with a musical instrument having varying numbers ofstrings corresponding to different notes, a magnetic pickup for eachnote, each said pickup having pole pieces including a permanent magnetthin in relation to its width, a core of soft magnetizable material thinin relation to its width and surrounded by a pickup coil, each pickuppermanent magnet and core being secured to a magnetizable plate of softmaterial in such relation to the strings of the note with which thepickup is intended to cooperate that the dimension of the pickup polepieces measured transversely of the strings will correspond with thetransverse distance across said strings.

6. In combination with a musical instrument having varying numbers ofstrings corresponding to different notes, a magnetic pickup for eachnote, each said pickup having pole pieces including a permanent magnetthin in relation to its width, a core of soft magnetizable material thinin relation to its width and surrounded by a pickup coil, each pickuppermanent magnet and core being secured to a magnetizable plate of softmaterial in such relation to the strings oi the note with which thepickup is intended to cooperate that the dimensions of the pickup polepieces measured transversely of the strings will correspond with thetransverse distance across said strings, all of said pickups havingsimilar magnets and similar cores.

GALAN W. DEMUTH.

